1. Field of the Invention
The present invention relates to a bicycle hub, more particularly to a bicycle hub that is provided with a seal member for preventing entrance of dust.
2. Description of the Related Art
Referring to FIG. 1, a conventional bicycle hub is shown to include a spindle 2 and a hub housing 1 mounted rotatably around the spindle 2 in such a manner that right and left spindle portions of the spindle 2 project outwardly from left and right end portions of the hub housing 1. The housing 1 has an annular groove 101 that is formed in the left end portion thereof and that is defined by a side wall 1012 and a bottom wall 1011. A sprocket mounting member 3 is sleeved around the left spindle portion of the spindle 2 adjacent to the left end portion of the hub housing 1. The sprocket-mounting member 3 includes an inner shell 302 which extends into and which is coupled securely with the left end portion of the hub housing 1, and an outer shell 301 which is rotatably mounted on the inner. shell 302 and which is formed with a circumferential groove 307. A ratchet mechanism is disposed within the outer shell 301, and is operably coupled with the inner shell 302 so as to permit synchronous rotation of the outer shell 301 with the hub housing 1 only in a forward direction.
A seal member 4 is disposed between the sprocket-mounting member 3 and the hub housing 1, and includes a circular tubular portion 401 that has an inner surface 4011 and that is disposed within the circumferential groove 307 of the outer shell 301, and an outward flange 402 which has a proximate inner end 4021 integrally formed with the tubular portion 401 and a distal outer end 4022 abutting against the side wall 1012 of the annular groove 101 in the hub housing 1, thereby preventing dirt or dust from entering into the sprocket-mounting member 3 and the hub housing 1.
Referring to FIG. 2, another conventional bicycle hub is shown to include a hub housing 5 mounted rotatably around a spindle 6, and a bearing retention cap 7 which is disposed within the left end portion 501 of the hub housing 5 around the left spindle portion thereof to prevent removal of a bearing unit from the hub housing 1. The bearing retention cap 7 has an outer surface 701 that is formed with an annular groove 7011. A seal member 8 includes a tubular portion 801 with an axial inner end 8011 disposed within the annular groove 7011 in the cap 7, and an outward flange 802 that extends radially and outwardly from the axial inner end 8011 and that abuts against an inner surface of the hub housing 5 so as to prevent dirt or dust from getting into an interior of the hub housing 5.
Note that in the aforesaid conventional bicycle hubs, the seal members 4, 8 are disposed fixedly on the sprocket-mounting member 3 and the bearing retention cap 7, respectively, and have portions slidably engaged with the inner surfaces of the hub housings 1, 5. As such, frictional force generated from the hub housings 1, 5 is relatively high due to the fact that the hub housings 1, 5 have a relatively large inner diameter that results in an increase in the interengaging surface area between the seal members 4,8 and the elements 3, 7.
Therefore, the object of this invention is to provide a bicycle hub which includes a flexible seal member of a specific configuration so as to be able to reduce frictional force generated due to rotation a hub housing relative to a spindle that is disposed within the hub housing.
Accordingly, a bicycle hub of the present invention includes a spindle, a tubular hub housing, at least one tubular end piece, and a tubular seal member. The hub housing is sleeved rotatably on the spindle. The end piece is sleeved fixedly on the spindle near an end of the hub housing. The seal member is disposed between the hub housing and the end piece. The hub housing has an end surface which is formed with an annular groove that is defined by a side wall and a bottom wall. The end piece has a tubular insert portion with an annular frictional outer surface, around which the side wall of the hub housing is disposed. The seal member is disposed within the hub housing, and includes an L-shaped cross-sectioned flexible outer ring, and a generally truncated conical inner ring. The outer ring has a circular tubular portion with an axial inner end, and an inward flange that extends integrally, radially and inwardly from the axial inner end of the circular tubular portion and that abuts against the bottom wall of the hub housing. The inner ring has a largest-diameter inner end that is formed integrally with an inner periphery of the inward flange of the outer ring, and a smallest-diameter outer end portion which is sleeved around and which is in tight engagement with the frictional outer surface of the end piece. The inner ring reduces gradually in inner diameter from the largest-diameter inner end to the smallest-diameter outer end portion. The smallest-diameter outer end portion has an inner diameter that is slightly smaller than the outer diameter of the insert portion of the end piece when removed from the end piece.
Accordingly, the seal member is fixed relative to the hub housing and is slidable relative to the end piece. During rotation of the hub housing relative to the spindle, because the outer diameter of the end piece is relatively small, friction force between the seal member and the end piece is thus reduced.